An easily-portable and non-volatile read/write memory module or cartridge is useful in many electronic applications. Such applications include ones in which it is advantageous to physically associate electrically-stored information or data with a tangible object that may be moved from place to place. In such applications, the function of the portable memory is similar to that of a tag. For ease of interconnection, compactness, and reliability, it is desirable that a portable memory module have a minimum number of terminals for removable connection to a host electronic system. Another useful feature for a portable memory module is a means for preventing unauthorized access to the data stored in the module.
In the past, various portable, non-volatile memory modules or cartridges have been devised. One such cartridge comprises a plastic housing having mounted therein a read-only memory integrated circuit mounted on a printed circuit board. Electrical terminals of the read-only memory integrated circuit are connected via conductors on the printed circuit board to terminals on an edge of the printed circuit board. The edge terminals of the printed circuit board are recessed in an opening at one side of the plastic housing and are adapted to be plugged into a multi-pin socket of a host electronic system. This cartridge requires connection to more than twenty terminals. Moreover, data cannot be electrically written to the memory of such a cartridge.
Other non-volatile memories include EPROMS (ultraviolet light erasable and electrically programmable read-only memories) and EEPROMS (electrically erasable and electrically programmable read-only memories). The long time typically required to modify data or information stored in such memories is unacceptable for certain applications.
Non-volatile memory modules having read/write memory (RAM) have also been devised. One such portable, non-volatile memory includes lithium batteries piggybacked onto a 2K.times.8 static CMOS RAM which is packaged in a 24-pin dual-in-line package. Such a package--having a large number of exposed pins or terminals--is not well-suited for portable use.
The above-described prior art memory modules typically require connection from the host electronic system to considerably more than five terminals of the module. It is advantageous, however, to have a smaller number of required terminals. For a reduced number of terminals, serially-accessible RAMS have been devised. One such memory is a CMOS static RAM organized 128.times.8 and packaged in an 8-pin dual-in-line package with no battery attached and with no standby power control logic included therein. Data is transferred to and from the RAM using synchronous serial communication. Seven pins of the package are utilized: an operating power supply input pin, a ground pin, a serial clock pin, two chip-enable pins, a data-input pin, and a data-output pin. The first 8-bit byte serially transferred after the chip is enabled is an input command byte that defines the starting RAM address and whether subsequent transfers are to be reads or writes. For multiple transfers (burst mode) the RAM address automatically increments as long as the RAM remains enabled. For this memory module, no provision is made to prevent unauthorized access.
It is known in the prior art that further pin or terminal reduction can be accomplished by combining the input and output pins into a single I/O pin. Additionally, it is heretofore known to provide only one chip enable input rather than two. Furthermore, it should be apparent that the serial clock input pin could be eliminated if asynchronous serial communication, rather than synchronous, were desirable or acceptable for a particular application.
None of the above-mentioned prior art approaches for portable, non-volatile memory, however, have proposed elimination of the operating power supply input pin. In this regard, it is important to distinguish an operating power supply input from a standby power supply input. In connection with providing non-volatility to a RAM integrated circuit, it has been proposed in the prior art to eliminate a standby power supply input pin by using a write enable pin to provide standby power; a conventional power supply input pin, though, provides operating power whenever the RAM is not in the standby mode.
In accordance with the foregoing, a need exists for a portable, non-volatile read/write memory module having a reduced number of pins or terminals for interconnection to a host electronic system. A need also exists for preventing unauthorized access to data stored in such a memory module